The right answer are all the three of them (1, 2 and 3).
Let's compare between a normal cell culture and a cancer cell culture:
- Normal or defined cultures: the cells only multiply during a limited number of degenerations (30 to 50 subcultures) then die: their life and their death is programmed. We then observe a decrease in their rate of proliferation, phase of senescence.
- Continuous culture or transformed or immortal lineages. The multiplication speed does not decrease (reproduction without limits, non-stop), which allows an indefinite number of subculture. The cells constituting these cultures lose the contact inhibition and grow in clusters or multilayer (multiple layers).
